Electron gun for a cathode ray tube

Abstract: A deformation produced by heat when a G1 grid is welded can be suppressed. A U-shaped slit (34) is formed on an outer peripheral wall (31) of a G1 grid (12). A spot-welding portion (X) is set to an end edge of a joint portion of the U-shaped slit (34) and this spot-welding portion (X) is spot-welded to a retainer (22) of a cathode (21) by a laser beam. In the G1 grid (12), the deformation produced by heat upon welding is absorbed by the surrounding portions of the slit (34). Therefore, it becomes possible to prevent the opposing surface opposing a G2 grid (13) from being expanded by heat. Thus, the spacing between the electrodes can be maintained to be a proper one and the angles of the electron beam emitting apertures can be maintained at proper ones. Therefore, it becomes possible to prevent the characteristic of the electron gun and the resolution of the cathode ray tube from being deteriorated.

Description: The invention relates to an electron gun for use with a cathode ray tube. Heretofore, in a cathode ray tube (CRT), three electron beams E are emitted from a unipotential electron gun 10, shown in FIG. 1 of the accompanying drawings, for example, to impinge on a three-primary color phosphor screen formed on the surface of the cathode ray tube to display a predetermined color. FIG. 1 shows an example of such conventional unipotential electron gun 10. Because the three-primary color phosphor screen is divided to provide very small phosphor screen parts, if the electron beams E are not impinged upon the phosphor screen at the precise positions, a mis-registration occurs so that a color is not displayed correctly. Therefore, the three electron beams E should be accurately emitted from predetermined positions of the electron gun 10. As shown in FIG. 1, the electron gun 10 comprises a support pin 11, a G1 grid (first grid) 12 through G5 grid (fifth grid) 17 and a convergence plate (deflection plate) 18. The respective assembly parts 11 through 18 are spaced apart with proper spacings. Long glass beadings 20 are secured to pins 19 projected from respective side walls, whereby the respective assembly parts 11 through 18 are properly positioned and then fixed with predetermined spacings. In order to accurately emit the electron beams E from the predetermined positions of the electron gun 10, the respective grids 12 to 17 should be assembled with a highly accurate relative positional relationship. The G1 grid 12 houses therein a cathode 21 as shown in FIG. 2. The cathode 21 has a retainer 22 fitted into a very small clearance produced between it and an outer peripheral wall 31 of the G1 grid 12. The outer peripheral wall 31 of the G1 grid 12 is spot-welded at its four spot-welding points X to the retainer 22 by some suitable welding means, such as laser beam or the like, as shown in FIGS. 3A, 3B. A ceramic disk 23 (see FIG. 2) is fitted and secured into the retainer 22. The ceramic disk 23 includes thereon three cathode sleeves 24 for emitting the electron beams E and three guide pins 25 for supporting the cathode sleeves 24. Each of the cathode sleeves 24 is fixed to the guide pin 25 by means of a V-tab having a V-letter wire (not shown). In the conventional electron gun 10, the outer peripheral portion 31 of the G1 grid 12 is spot-welded to the retainer 22 by a laser beam and the surrounding portion of the spot-welding portion is heated by a large quantity of heat generated upon spot-welding so that an opposing surface 32 that opposes the G2 grid 13 is expanded by about 20 to 30 µm, for example, as shown in FIG. 4. An expanded amount 6 obtained at that time is fluctuated with an intensity of a laser output power used when the outer peripheral wall 31 of the G1 grid 12 is spot-welded to the retainer 22. Specifically, the expanded amount 6 is increased as the intensity of the laser output power is increased. When the G1 grid 12 is expanded at its opposing surface 32 opposing the G2 grid 13, the spacing between the G1 grid 12 and the G2 grid 13 is changed so that a cut-off voltage of the electron beam E is fluctuated. There is then the disadvantage that the characteristic of the electron gun 10 is deteriorated. Further, although the three electron beams E are emitted from the electron gun 10, an angle of the surface in which side beam apertures 33 to emit two side electron beams E are provided is changed so that the path of the electron beam E is displaced. There is then the disadvantage that the cathode ray tube is deteriorated in resolution. Patent Specification US-A-3 716 739 discloses means for supporting and shielding a compact electron gun in a cathode ray tube wherein a skirted annular member is supported within the neck of the tube and has slits both in a skirt portion and in a planar portion extending towards the axis to reduce pick up of an excessive amount of induction heat. According to the invention there is provided an electron gun for a cathode ray tube in which a cathode is fitted into the inside of a grid and an outer peripheral wall of said grid is welded to a retainer of said cathode, comprising: cutouts formed on said outer peripheral wall of said cathode for absorbing a deformation generated by heat, wherein end edge portions of said cutouts or portions surrounding said cutouts are welded to said retainer. In such an electron gun for a cathode ray tube a characteristic of an electron gun can be prevented from deterioration and the cathode ray tube can be prevented from deterioration. The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which: FIG. 1 is a diagram showing an arrangement of a previously proposed unipotential electron gun; FIG. 2 is a perspective view showing an arrangement of a G1 grid of the electron gun shown in FIG. 1; FIG. 3A is a side view of the G1 grid seen from an arrow A direction of FIG. 2, and to which reference will be made in explaining the welding positions of the G1 grid; FIG. 3B is a side view of the G1 grid seen from an arrow B direction of FIG. 2, and to which reference will be made in explaining the welding positions of the G1 grid; FIG. 4 is a diagram used to explain a deformation produced in the G1 grid of the conventional electron by heat; FIG. 5 is a perspective view showing an arrangement of the G1 grid of the electron gun according to an embodiment of the invention; FIG. 6A is a side view of the G1 grid seen from an arrow A direction of FIG. 5, and to which reference will be made in explaining the welding positions of the G1 grid; FIG. 6B is a side view of the G1 grid seen from an arrow B direction of FIG. 5, and to which reference will be made in explaining the welding positions of the G1 grid; FIG. 7 is a diagram used to explain a spot-welding portion according to the invention more in detail; FIG. 8 is a graph used to explain a relationship between an intensity of a laser output power used upon welding and an expanded amount; and FIGS. 9A to 9C are diagrams used to explain other embodiments of the G1 grid according to the invention, respectively. An electron gun according to embodiments of the invention will hereinafter be described with reference to the accompanying drawings, in which elements and parts identical to those of FIGS. 1 to 4 are marked with the same references and therefore need not be described in detail. FIG. 5 shows an arrangement of the G1 grid (first grid) 12 of the electron gun of the invention. The G1 grid 12 can be applied to the electron gun 10 shown in FIG. 1. As shown in FIG. 5, the G1 grid 12 includes U-shaped slits 34 defined in the outer peripheral wall 31. The U-shaped slit 34 is disposed at its slit joint portion 35 on the opposing surface 32 opposing the G2 grid 13 and four U-shaped slits 34 are disposed at four proper positions on the outer peripheral wall 31 of the G1 grid 12 as shown in FIGS. 6A, 6B. As shown in FIG. 7, a spot-welding portion X is set to an end edge of a projected portion 37 surrounded by two side edge portions 36 of the U-shaped slit 34 and the slit joint portion 35. This spot-welding portion X is spot-welded to the retainer 22 of the cathode 21 fitted into the G1 grid 12 by some suitable means, such as a laser beam or the like. In the G1 grid 12, even though the spot-welding portion X and the surrounding portion of the spot-welding portion X are heated by a laser beam upon spot-welding, a deformation produced by heat is absorbed on the portion surrounding the U-shaped slit 34 and the portions spaced apart from the U-shaped slit 34 can be prevented from being deformed by heat. Unlike the example of the conventional electron gun shown in FIG. 4, it is possible to prevent the opposing surface 32 opposing the G2 grid 32 from being expanded. FIG. 8 is a graph used to explain a relationship between an intensity of a welding laser output power in the G1 grid 12 and the expanded amount δ (FIG. 4) of the opposing surface 32 opposing the G2 grid 13. FIG. 8 shows measured experimental results of the laser output powers and the expanded amount δ. Study of FIG. 8 reveals that, while the expanded amount δ in the conventional G1 grid 12 was about 26 µm when the intensity of the laser output power was 880V, the expanded amount δ in the G1 grid 12 of the inventive electron gun was considerably decreased to about 7 µm when the intensity of the laser output power was similarly 880V. If the intensity of the laser output power is decreased, then the expanded amount δ also is decreased more. However, if the intensity of the laser output power were too low, the welding could not be made with a laser output power of 680V according to this embodiment. While the spot-welding portion X is set to the end edge of the projected portion 37 surrounded by the joint portion 35 and the two side edge portions 36 of the U-shaped slit 34 as described above, the present invention is not limited thereto and the following variants are also possible. Specifically, as shown in FIG. 9A, the spot-welding portion X may be set to a central portion of the projected portion 37. Further, as shown in FIG. 9B, a slit 34A may be formed on the outer peripheral wall 31 of the G1 grid 12 and the spot-welding portion X may be set to the end edge portion of the bottom portion of the slit 34A. Furthermore, as shown in FIG. 9C, two slits 34B, 34B are parallelly formed on the outer peripheral wall 31 and the spot-welding portion X may be set to a central portion of the two slits 34B, 34B. Since the G1 grid 12 and the retainer 22 of the cathode 21 are welded to each other as described above, the deformation produced by heat is absorbed by the surrounding portions of the slits 34, 34A, 34B and therefore the opposing surface 32 opposing the G2 grid 13 can be prevented from being expanded. As set forth, the first grid includes the slit defined in the outer peripheral wall thereof and the end edge portion of the central portion of the slit is welded to the retainer of the cathode. Therefore, the deformation produced by heat generated upon welding is absorbed by the surrounding portions of the slit and the portions spaced apart from the slit are not deformed by heat so that the spacing between the G1 grid and the G2 grid can be maintained with the proper dimensions. Thus, it becomes possible to prevent the characteristic of the electron gun from being deteriorated. Furthermore, since the emitting apertures of the electron beams are held at the predetermined angle, it becomes possible to prevent the resolution of the cathode ray tube from being deteriorated.

Claims: An electron gun (10) for a cathode ray tube in which a cathode (21) is fitted into the inside of a grid (12) and an outer peripheral wall (31) of said grid (12) is welded to a retainer (22) of said cathode (21), comprising: cutouts (34) formed on said outer peripheral wall (31) of said cathode (21) for absorbing a deformation generated by heat, wherein end edge portions (37) of said cutouts (34) or portions surrounding said cutouts (34) are welded to said retainer (22). An electron gun according to claim 1, wherein said grid (12) is a first grid. An electron gun according to claim 1, wherein said cutouts (34) are in the shape of a letter U. An electron gun according to claim 1, wherein said cutouts are two parallel slits (34B). An electron gun according to claim 1, wherein said cutouts are U-shaped slits (34).

Inventors: ENDO NOBUYUKI, ENDO, NOBUYUKI, ENDO, NOBUYUKI, C/O INT. PROP. DIV., SONY CORP.
Applicants: SONY CORP, SONY CORPORATION
Application year: 1994
Main classification: H01J29
IPC codes: H01J29